The present invention comprises a new and distinct hybrid spiraea cultivar hereinafter referred to by the cultivar name ‘NCSX1’. This new spiraea was developed through a breeding program at North Carolina State University, Mills River, N.C. ‘NCSX1’ was selected from a population of seedlings grown from a controlled cross of Spiraea japonica H2007-101-003 (unpatented, tetraploid)×Spiraea ‘Zelda’ (U.S. Plant Pat. No. 21,976 P2, diploid). The first asexual propagation of ‘NCSX1’ was carried out in July 2012 by rooting stem cuttings at the North Carolina State University, Mountain Horticultural Crops Research Station, Mills River, N.C. and has been asexually reproduced repeatedly by vegetative cuttings over a 3 year period. ‘NCSX1’ roots readily from softwood cuttings treated with a basal dip of 4,000-5,000 ppm indole butyric acid (potassium salt) in water. ‘NCSX1’ has been found to retain its distinctive characteristics through successive asexual propagations.